N-linked glycans are found attached to asparagine amino acids on many proteins produced by organisms. They are responsible for many structural and functional aspects of glycoproteins, including cell-cell interactions, intracellular trafficking, and affecting the solubility and stability of proteins in vivo. During protein synthesis, these glycans have also shown to affect protein folding and the intracellular transport within the cells.
N-linked glycans are classified into three sub-types: high mannose, complex, and hybrid.
All N-linked glycans consist of a conserved pentasaccharide core consisting of a linear chain of two N-Acetylglucosamine (GlcNAc) moieties attached to a mannose which branches out with two additional mannose residues. This is also referred to as the tri-mannosyl core.
Complex glycans are characterized by having a conserved structure consisting of a branched structure with two to four arms linked to the two mannose sugars of the conserved core. Each arm consists of the following linear structure [-GlcNAc-Galactose-Sialic acid] when synthesized to completion, though post-translation modification may truncate the structures prematurely and/or sugar residues may be lost over the lifespan of the glycoprotein. Fucosylation of the asparagine-linked GlcNAc residue is common, as well as the presence of a bisecting GlcNAc attached to branching tri-Mannose-GlcNAc-GlcNAc core.